The present invention generally relates to processing a semiconductor substrate. In particular, the present invention relates to a system and a method for regulating developer time and temperature.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist, application and maintaining a desired temperature of and time exposure to the developer are significant factors in achieving desired critical dimensions. The developer should be maintained at a uniform temperature in order to insure uniformity and quality of the underlying photoresist layer to be developed. Small changes in the time/temperature history of the developer can substantially alter image sizes, resulting in lack of image line controlxe2x80x94a few degrees in temperature difference may drastically affect critical dimensions. For example, often substantial line size deviations occur when the developer temperature is not maintained within 0.5 degree tolerance across a silicon wafer. Likewise, uniform time exposure to the developer solution cannot compensate for variations at center to edge portions of a wafer. For example, printed gratings of a desired size often correspond to a mixture of sizes due to the center to edge variations across the wafer. That is, printed gratings may not be properly formed in a thicker portion of the wafer as opposed to a thinner portion of the wafer.
Thus, there is an unmet need for an efficient system/method to maintain developer time and temperature in order to increase fidelity in image transfer. There is also an unmet need for a system/method to compensate for center to edge variations in a wafer.
The present invention provides for a system and method which facilitates controlling developer temperature and time. More specifically, the system and method employ a non-destructive measuring system to monitor parameters of the developer which vary with respect to the temperature of the developer. This is accomplished in part by employing a plurality of optical fibers arranged to project radiation on respective portions of the developer. The radiation reflected from the developer is indicative of at least one of several parameters of the developer (e.g., thickness, color and absorption) which vary in correlation with developer time and temperature. For example, a plurality of heaters are arranged to each correspond to a particular developer portion, respectivelyxe2x80x94each heater is responsible for heating the particular developer portion. The developer temperature is monitored by the system, and the heaters are selectively driven by the system so as to maintain developer temperature at a desired level. As a result, substantial uniformity in developer temperature is achieved, which in turn increases fidelity of image transfer. Similarly, developer time is optimized in order to compensate for variations in the center to edge regions of the wafer.
One aspect of the present invention relates to a system for regulating in-situ developer temperature. The system includes at least one lamp operative to heat a portion of a developer; a lamp driving system for driving the at least one lamp; a system for directing radiation to the portion of the developer; a measuring system comprising a UV/Vis spectrophotometry system for measuring parameters of the developer based on radiation reflected from the developer; and a processor operatively coupled to the measuring system and a lamp driving system, the processor receiving developer parameter data from the measuring system and the processor using the data to at least partially base control of the at least one lamp so as to regulate temperature of at least a portion of the developer.
Another aspect of the present invention relates to a method for regulating in-situ developer temperature and exposure time. The method involves the steps of defining a substrate as a plurality of portions; defining a developer deposited over the substrate as a plurality of portions; directing radiation having a wavelength from 190 nm to about 800 nm onto at least one of the portions of the substrate and of the developer; collecting radiation intensity reflected from the at least one portion corresponding to the substrate and to the developer; during development, analyzing the reflected radiation intensity to determine the temperature of the at least one portion of the developer and to determine image size of the at least one portion of the substrate; controlling a heating device to regulate the temperature of the developer portion; and controlling a timing mechanism to regulate the exposure time of the substrate portion.
Yet another aspect of the present invention relates to a method for regulating in-situ temperature and exposure time of a developer, the developer overlying a substrate comprising an image pattern. The method involves the steps of partitioning the developer into a plurality of grid blocks; using a plurality of heaters to heat the developer, each heater functionally corresponding to a respective grid block; using a plurality of timers to time the exposure time of the developer, each time sensor corresponding to a respective grid block; determining temperatures corresponding to the respective grid blocks of the developer using a UV/Vis spectrophotometry system; determining exposure times corresponding to the respective grid blocks of the developer using a UV/Vis spectrophotometry system; and using a processor to coordinate control of the heaters and timers, respectively, in accordance with determined temperatures and exposure times of the respective grid blocks of the developer.
Still yet another aspect of the present invention relates to a system for regulating in-situ temperature of a developer means for defining a substrate as a plurality of portions. The system includes means for defining a developer deposited over the substrate as a plurality of portions; means for directing radiation having a wavelength from 190 nm to about 800 nm onto at least one of the portions of the substrate and of the developer; means for collecting radiation intensity reflected from the at least one portion corresponding to the substrate and to the developer; during development, means for analyzing the reflected radiation intensity to determine the temperature of the at least one portion of the developer and to determine image size of the at least one portion of the substrate; means for controlling a heating device to regulate the temperature of the developer portion; and means for controlling a timing mechanism to regulate the exposure time of the substrate portion.